1. Field of the Invention
The present invention relates to a propeller fan provided in the vicinity of a heat exchanger of an in-vehicle air conditioner. More particularly, the present invention relates to a propeller fan capable of improving ventilation efficiency and reducing noise in an in-vehicle heat exchanger such as a radiator and a condenser.
2. Description of the Related Art
A propeller fan for vehicle such as a fan of a radiator for vehicle and a fan for cooling a condenser of in-vehicle air conditioner is generally composed of a rotary vane wheel and a shroud casing. These propeller fans are required to be placed into a narrow engine room and to have lightweight. This requires the propeller fans to be downsized in depth dimension in a flow direction. Furthermore, the radiator and the condenser to be cooled are required to be small and to have a high heat exchanging performance. This makes ventilation resistance large, so that the propeller fan for vehicle is in an operating condition of a high static pressure difference. In such a high static pressure type propeller fan with a casing, it is known that a clearance dimension between the casing and a rotary vane tip (tip clearance, hereinafter, merely referred to as clearance) is an important dimension which exerts an influence on air blowing performance, efficiency and noise.
Conventionally, for the clearance, there has been a technique of protruding rotary vanes on the upstream side of a bell mouth in order to efficiently take in a centripetal flow. Furthermore, there have been provided various techniques, such as a technique of integrating a ring bell mouth with rotary vanes in order to make the clearance zero for the purpose of corresponding to the operation condition of high static pressure (for example, Japanese Patent Application Laid-Open No. 2004-176702).
Furthermore, as described above, the propeller fan cannot have a large dimension in the depth direction (thickness direction). Therefore, a shroud cross-sectional shape from a rectangular radiator and the like to a circular fan inlet port changes precipitously, which remarkably limits an air rectification effect. Particularly, in the bell mouth portion provided at the fan inlet portion is often constructed with an angle R of a small radius R (chamfering). Therefore, most air passing through the rectangular radiator or the like easily becomes a centripetal flow toward the center portion of the fan by inertial force. This reduces an effective radius of the fan. Furthermore, this leads to deterioration of air blowing performance, and efficiency and increase of noise.
In order to avoid the above-described deterioration of the air blowing performance and the like, there has been conventionally applied a bell mouth having an elliptic angle R or a bell mouth in which a main portion of a bell mouth is constructed with a relatively large angle R and only a portion thereof interfering with a propeller fan has a small angle R (for example, Japanese Patent Application Laid-Open No. 2001-349300).
However, even in the above-described techniques, no sufficient effect cannot be obtained, and has an adverse effect that discrete frequency noise caused by interaction between the rotary vane wheel of the propeller fan and the shape of the shroud is prominent, and so on. Furthermore, although the above-described techniques have an effect of improving the individual performance of air blowing characteristics, efficiency or the like, there has been provided no effective technique that can improve all of the air blowing characteristics, efficiency and suppression ratio of noise in a balanced manner.